14.1
\nA Balanced Introduction to Computer Science, 3\/E
\nDavid Reed \u00a9Pearson Prentice Hall, 2011
\nChapter 14 Review Question Solutions
\n14.1. What would happen if you placed the number 100 in R0, then set the knobs so that A
\nBus = R0, B Bus = R0, ALU = A-B, and C Bus = R0?
\nThe value in Register 0 would be subtracted from itself and the result, 0, stored back
\ninto Register 0.
\n14.2. Describe the settings that would cause the value stored in R2 to be doubled.
\nA Bus = R2, B Bus = R2, ALU = A+B, and C Bus = R2.
\n14.3. How many cycles are required to add the contents of R0, R1, and R2 and then place
\nthe sum in R3? Describe the settings for each cycle.
\nA Bus = R0, B Bus = R1, ALU = A+B, C Bus = R3.
\nA Bus = R2, B Bus = R3, ALU = A+B, C Bus = R3.
\n14.4. What settings would result in the sum of registers R0 and R3 being stored in memory
\nlocation 4?
\nA Bus = R0, B Bus = R3, ALU = A+B, C Bus connected to MM, R\/W = 4.
\n14.5. What settings would cause the contents of memory address 4 to be copied into
\nregister R0?
\nMM Bus connected to C, C Bus = R0, R\/W = 4.
\n14.6. Assuming that data can be copied to and from main memory in a single CPU cycle,
\nhow many cycles are required to add the contents of memory addresses 5 and 6 and
\nthen store the result in memory address 7? Describe the settings for each cycle.
\nMM Bus connected to C, C Bus = R0, R\/W = 5.
\nMM Bus connected to C, C Bus = R1, R\/W = 6.
\nA Bus = R0, B Bus = R1, ALU = A+B, C Bus connected to MM, R\/W = 7.
\n14.7. What task would the following machine-language program perform?
\n0: 1010001000000000
\n1: 1000001000000011
\n14.2
\n2: 1111111111111111
\nThis program stores the value 0 in memory address 3. The first statement subtracts
\nthe value in R0 from itself, and stores the result (0) back in R0. The second statement
\nstores the value from R0 in MM[3]. The third statement halts execution.
\n14.8. What sequence of machine-language instructions would cause the contents of the four
\nregisters to be copied into memory locations 7, 8, 9, and 10, respectively?
\n1000001000000111
\n1000001000101000
\n1000001001001001
\n1000001001101010
\n1111111111111111
\n14.9. What sequence of machine-language instructions would cause the simulator to add
\nthe contents of memory locations 10, 11, and 12 and then store the result in memory
\nlocation 13?
\n1000000100001010
\n1000000100101011
\n1000000101001100
\n1010000100110001
\n1010000100111011
\n1000001001101101
\n1111111111111111
\n14.10. What do you think would happen if you forgot to place a HALT instruction at the end
\nof a machine-language program? How would the Control Unit react? Use the
\nsimulator to test your prediction, then report the results.
\nThe Program Counter would advance beyond the last instruction. The contents of
\nmemory addresses would be treated as instruction codes, either producing unexpected
\nresults or an error if the code does not correspond to a legal instruction.
\n14.11. What sequence of assembly-language instructions corresponds to the machinelanguage
\ninstruction set from Exercise 14.7?
\nSUB R0 R0 R0
\nSTORE 3 R0
\nHALT
\n14.12. What sequence of assembly-language instructions corresponds to the machinelanguage
\ninstruction set you wrote in Exercise 14.9?
\nLOAD R0 10
\nLOAD R1 11
\nLOAD R2 12
\n14.3
\nADD R3 R0 R1
\nADD R3 R2 R3
\nSTORE 13 R3
\nHALT
\n14.13. Write a sequence of assembly-language instructions that multiplies the contents of
\nmemory location 10 by four. For example, if the number 10 were stored in memory
\nlocation 10, executing your instructions would cause the simulator to store 40 there.
\nNote: although the ALU Operation knob does not provide a multiplication setting, a
\nnumber can be multiplied via repeated additions (e.g., 10* 4 = 10+10+10+10).
\nLOAD R0 10
\nADD R0 R0 R0
\nADD R0 R0 R0
\nSTORE 10 R0
\nHALT
\n1. TRUE or FALSE? Any piece of memory that is used to store the sum of numeric values
\nis known as a register.
\nFALSE
\n2. TRUE or FALSE? The path that data follows within the CPU, traveling along buses
\nfrom registers to the ALU and then back to registers, is known as the CPU datapath.
\nTRUE
\n3. TRUE or FALSE? All modern CPUs provide the same set of basic operations that can be
\nexecuted in a single CPU cycle.
\nFALSE
\n4. TRUE or FALSE? The size of main memory is generally measured in MHz or GHz.
\nFALSE
\n5. TRUE or FALSE? Suppose you wish to add two numbers that are stored in memory.
\nBefore the Arithmetic Logic Unit (ALU) can add the numbers, they must first be
\ntransferred to registers within the CPU.
\nTRUE
\n14.4
\n6. TRUE or FALSE? In real computers, it takes roughly the same amount of time to
\ntransfer data from main memory to registers as it does to add two numbers in registers.
\nFALSE
\n7. TRUE or FALSE? Within the CPU, the Control Unit is responsible for fetching
\nmachine-language instructions from memory, interpreting their meaning, and carrying
\nout the specified CPU cycles.
\nTRUE
\n8. TRUE or FALSE? Suppose a CPU contains eight registers. Within a machine-language
\ninstruction, at least three bits would be required to uniquely identify one of the registers.
\nTRUE
\n9. TRUE or FALSE? In a multitasking computer, the program counter keeps track of how
\nmany programs are currently loaded into main memory.
\nFALSE
\n10. TRUE or FALSE? In a stored-program computer, both machine-language instructions
\nand the data operated on by those instructions can reside in main memory at the same
\ntime.
\nFALSE
\n11. Name the three subunits of the CPU, and describe the role of each subunit in carrying out
\ncomputations.
\nThe arithmetic logic unit (ALU) is the collection of circuitry that performs actual
\noperations on data. Registers are memory locations that are built into the CPU and
\naccessed directly by the ALU. The control unit is the circuitry in charge of fetching data
\nand instructions from main memory, as well as controlling the flow of data from the
\nregisters to the ALU and back to the registers.
\n12. Describe how data values move around the CPU datapath and what actions occur during
\na single CPU cycle. How does the datapath relate to CPU speed?
\nThe path that data follows within the CPU, traveling along buses from registers to the
\nALU and then back to registers, is known as the CPU datapath. Every task performed by
\na computer, from formatting a document to displaying a page in a Web browser, is
\nbroken down into sequences of simple operations; the computer executes each individual
\noperation by moving data from the registers to the ALU, performing computations on that
\n14.5
\ndata within the ALU, and then storing the result in the registers. CPU speed measure
\nhow many such cycles occur in one second, e.g., 1.8 GHz means 1.8 billion CPU cycles
\nper second.
\n13. Consider two computer systems that are identical except for their CPUs. System 1
\ncontains a 1.8 GHz Pentium 4, whereas System 2 contains a 1.8 GHz PowerPC processor.
\nWill these two systems always require the same amount of time to execute a given
\nprogram? Justify your answer.
\nCPU speed is generally measured in gigahertz (GHz), which indicates how many billions
\nof CPU cycles occur in a second. Since different families of CPUs will different basic
\noperations using different hardware configurations, some tasks may require more cycles
\nusing one CPU when compared with another. Thus, performance comparisons based on
\nCPU speed are not always accurate.
\n14. Consider the following tasks: (1) adding 100 numbers stored in main memory, and (2)
\nadding a number to itself 100 times. Although both tasks require 100 additions, the
\nsecond would be executed much more quickly than the first would. Why?
\nFor the first task, the 100 numbers must each be loaded into registers from main memory
\nbefore the additions can take place. Thus, 100 memory loads and 99 additions must take
\nplace. For the second task, only one number must be loaded from memory, before
\nadditions can take place. Thus, 1 memory load and 99 additions must take place.
\n15. Machine languages are machine-specific, meaning that each type of computer has its own
\nmachine language. Explain why this is the case.
\nMachine language instructions correspond to the low-level operations that can be
\nexecuted by the hardware of the machine. Since different computers have different
\nCPUS, register configurations, and ALU operations, their machine languages will differ.
\n16. Within the control unit, what is the role of the program counter (PC)? That is, how is the
\nPC used in fetching and executing instructions?
\nThe program counter (PC) keeps track of the address of the next program instruction to
\nbe executed. Initially set to the first instruction in the program, it is automatically
\nincremented as each instruction is loaded, decoded by the control unit, and executed.
\n17. In a stored-program computer, both instructions and data are stored in main memory.
\nHow does the Control Unit know where the program instructions begin? How does it
\nknow where the instructions end?
\nIn real computers, the starting location for programs is usually maintained by the
\noperating system, which keeps track of each program in memory and its location. The
\n14.6
\nend of a program is usually marked by a special instruction that tells the control unit to
\nHALT.
\n18. Describe two advantages of assembly languages over machine languages.
\nIt is much easier for programmers to remember and understand assembly-language
\ninstructions than patterns of 0s and 1s. Furthermore, most assembly languages support the
\nuse of variable names, enabling programmers to specify memory locations by descriptive
\nnames, rather than by numerical addresses.<\/p>\n","protected":false},"excerpt":{"rendered":"
14.1 A Balanced Introduction to Computer Science, 3\/E David Reed \u00a9Pearson Prentice Hall, 2011 Chapter 14 Review Question Solutions 14.1. What would happen if you placed the number 100 in R0, then set the knobs so that A Bus = R0, B Bus = R0, ALU = A-B, and C Bus = R0? The value […]<\/p>\n","protected":false},"author":274,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"open","template":"","meta":{"_mi_skip_tracking":false},"_links":{"self":[{"href":"https:\/\/sites.evergreen.edu\/compcog15\/wp-json\/wp\/v2\/pages\/1450"}],"collection":[{"href":"https:\/\/sites.evergreen.edu\/compcog15\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sites.evergreen.edu\/compcog15\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sites.evergreen.edu\/compcog15\/wp-json\/wp\/v2\/users\/274"}],"replies":[{"embeddable":true,"href":"https:\/\/sites.evergreen.edu\/compcog15\/wp-json\/wp\/v2\/comments?post=1450"}],"version-history":[{"count":0,"href":"https:\/\/sites.evergreen.edu\/compcog15\/wp-json\/wp\/v2\/pages\/1450\/revisions"}],"wp:attachment":[{"href":"https:\/\/sites.evergreen.edu\/compcog15\/wp-json\/wp\/v2\/media?parent=1450"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}